The invention relates to a prosthetic foot of the energy-storing type, and a method of manufacturing same.
Until recently, prosthetic feet, ankles and lower legs available to lower limb amputees, have been primarily designed for walking and, hence, the structure of such conventional prostheses have failed to provide a natural lift and thrust effect for the more active and sports-minded person. Although some foot prostheses contain a form of energy absorption, such as various forms of metal springs or flexible foam located in the heel region, e.g., the "solid ankle cushion heel" or SACH foot, such devices do little more than absorb some of the pistoning or shock forces that would otherwise be transmitted to the amputee's stump. For walking, such prior art devices are at least acceptable; however, when the amputee attempts to walk briskly, or over long distances, run and jump, then the prosthesis has the feel of a "dead" foot lacking a natural quality of rebound or springback, and forward thrust necessary for athletic movement. As a result, excessive energy is required by the user to carry the foot along at an unnatural and, hence, uncomfortable gait.
Efforts have been made to construct a prosthetic foot that interacts dynamically with the cyclic loading and unloading of the foot by the amputee's body motions. One such prosthesis is known as the "FLEX-FOOT" manufactured by Flex-Foot, Inc., Salt Lake City, Utah, and comprises a combination lower leg and foot prosthesis in which the main structural member is made of aerospace graphite composites. The energy storage in the "FLEX-FOOT" prosthesis occurs in an elongate shaft portion extending upward from a midbody point of an enlarged foot portion, which also stores energy, and joining an enlarged upper prosthesis adapted for attachment to the stump. Such a prosthesis has advantages in overcoming some of the problems found in nonenergy-storing devices, however, the required elongate shaft portion extending between the foot and the upper prosthesis renders this device unusable when only a foot prosthesis is required, and when it is necessary or desirable to attach just a foot prosthesis to a standard lower leg fitting. Prosthesis modularity is important in accommodating the needs of a widely varying range of patient requirements.
One earlier attempt to provide a foot prosthesis that overcomes the above problems was made by a group headed by Dr. Ernest M. Burgess, one of the co-inventors herein, and is disclosed in a paper entitled "The Seattle Prosthetic Foot" appearing in Orthotics and Prosthetics Journal, Vol. 37, No. 1, Spring 1983. In that article, a prosthetic foot structure comprises a layup of fiberglass leaf springs in the shape of a cantilever structure with the secured end of the cantilever being joined or fastened to an upper prosthesis. The leaf springs, which are laminated, form a V-shaped bend between an attachment flange and a main forefoot portion, and a rubber deflection bumper is disposed in the "V" to cushion the compression of the "V" immediately under the point of attachment to the upper prosthesis. A cable connected between the attachment flange and the series of leaf springs prevents excessive extension (divergence of the "V" between the attachment flange and the leaf springs), and thereby minimizes the tendency of the structure to delaminate under certain use conditions. While testing of this early experimental foot showed promise, the structure itself was too heavy for most patients and the laminated spring structure did not prove sufficiently durable in service. Users also complained that the stiffness of the foot made slow walking difficult. The laminated epoxy/glass leaf spring design required considerable, direct assembly labor, and the adhesive bonding of the laminated structure added cost, weight and was the primary cause of the lack of durability of the foot.